Abstract

Pancreatic ductal adenocarcinoma (PDA) has the worst prognosis of all cancers and is the 4th leading cause of cancer-related deaths in the United States. Mucin1 (MUC1) is a transmembrane glycoprotein over-expressed in more than 60% of PDA and its expression correlates with high metastases and poor prognosis. In PDA, there is a correlation between blood vessel density, tumor levels of VEGF, and disease progression. We have recently discovered a novel association between MUC1 and neuropilin-1 (NRP-1) expression. Neuropilin-1 (NRP-1) is a co-receptor for VEGF165 and blockade of NRP-1-VEGF165 interaction has been shown to inhibit angiogenesis and tumor growth in several other cancer types. Thus, we hypothesize that MUC1 induces a pro-angiogenic tumor microenvironment by increasing levels of VEGF and NRP-1, thus enhancing disease progression and metastases. We have generated Muc1-expressing KC and Muc1-null KCKO mouse PDA cell lines for this study. Compared to KCKO, KC cells secrete more VEGF and express higher levels of NRP-1 as well as VEGF receptors (1/2/3). Although the cell culture supernatants from KC do not alter the NRP-1 level on the endothelial line 2H11 cells, they significantly promote the 2H11 cell tube formation. Consistent with the in vitro results, tumor lysates from KC-bearing mice have higher levels of NRP-1 and VEGFR2 and its phosphorylations at Tyr residues 951, 996, and 1175. In human PDA cell lines, inhibition of MUC1 expression by specific siRNA reduced NRP-1 level while overexpression of full-length MUC1 increases NRP-1 expression. This suggests a direct regulation of NRP-1 by MUC1. Furthermore, the over-expression of MUC1 in BxPC3 human PDA cell line induces strong angiogenesis and promotes tumor metastasis in a zebrafish tumor xenograft model. Finally, we report that inhibition of NRP-1 by its specific blocking peptide suppresses BxPC3.MUC1 tumor growth in vivo. Taking together, MUC1 in PDA cells can enhance their own NRP-1 levels and promote the VEGF-VEGFR-NRP-1 signaling, which may favor the creation of a pro-angiogenic microenvironment for tumor growth and metastases. Our findings highlight the potential for MUC1 targeted blockade of VEGF-NRP-1 interaction in PDA by conjugating the NRP-1 inhibitory agents to a MUC1 targeting antibody.